Bank spokeswoman Tara Burke emphasized that the outages, from 6:15 to 11:26 a.m. EDT Friday, were not related to the uproar over news of the $5 monthly debit-card fees. BofA's mobile and text banking services were unaffected, she added.

As the nation's largest retail bank, Bank of America also is believed to have the largest number of customers who use online banking services -- 29 million, Burke said. Reports of online outages are not uncommon, although Burke wouldn't say how frequently the system short-circuits.

She also wouldn't disclose how many customers were affected by Friday's outage or what caused it, saying only: "There were some issues, some customers have had trouble with access."

Bank of America spokeswoman Anne Pace declined to characterize the attitude of the customers who were bombarding the bank with questions at its branches, call centers and via Twitter.

"Most of them want to understand what this means for them and how it will impact their accounts," she said in an email. "We are doing our best to explain the impacts, the value and convenience the debit card offers and how to avoid the fee if necessary."

Short of taking out a BofA mortgage or depositing $20,000 with the Charlotte, N.C., bank, the way to avoid the fee is to avoid making purchases with debit cards and using them only for ATM transactions, which remain free.

Customers also could jump to another bank, of course, although major institutions such as Wells Fargo and JPMorgan Chase have been testing $3 monthly fees for debit cards.

Bank of America stock, meantime, sank by 14 cents, or 2.2%, to $6.21 in early afternoon trading in New York. It has been the worst performing stock of the 30 in the Dow Jones Industrial Average during the third quarter, having fallen 42% as of Wednesday's close of $6.35.